Remove foreign-key on create_uid and write_uid

Instead prevent delete of any user to keep logging information.

issue4925
review24301002

CHANGELOG

@@ -1,3 +1,5 @@
+* Remove foreign-key on create_uid and write_uid
+* Prevent deletion of any user
 * Manage PostgreSQL schema
 * Remove colors attribute on tree view
 * Remove style on Report

trytond/model/modelsql.py

@@ -188,7 +188,11 @@ class ModelSQL(ModelStorage):
                     ref = field.model_name.replace('.', '_')
                 else:
                     ref = pool.get(field.model_name)._table
-                table.add_fk(field_name, ref, field.ondelete)
+                if field_name in ['create_uid', 'write_uid']:
+                    # migration from 3.6
+                    table.drop_fk(field_name)
+                else:
+                    table.add_fk(field_name, ref, field.ondelete)
 
             table.index_action(
                 field_name, action=field.select and 'add' or 'remove')

trytond/res/user.py

@@ -103,12 +103,11 @@ class User(ModelSQL, ModelView):
             'groups',
         ]
         cls._error_messages.update({
-            'rm_root': ('You can not remove the root user\n'
-                    'as it is used internally for resources\n'
-                    'created by the system '
-                    '(updates, module installation, ...)'),
-            'wrong_password': 'Wrong password!',
-            })
+                'delete_forbidden': ('Users can not be deleted '
+                    'for logging purpose.\n'
+                    'Instead you must inactivate them.'),
+                'wrong_password': 'Wrong password!',
+                })
 
     @classmethod
     def __register__(cls, module_name):
@@ -267,11 +266,7 @@ class User(ModelSQL, ModelView):
 
     @classmethod
     def delete(cls, users):
-        if [u.id for u in users if u.id == 0]:
-            cls.raise_user_error('rm_root')
-        super(User, cls).delete(users)
-        # Restart the cache for _get_login
-        cls._get_login_cache.clear()
+        cls.raise_user_error('delete_forbidden')
 
     @classmethod
     def search_rec_name(cls, name, clause):